Vietnam's aviation authority has ordered the biggest airport Tan Son Nhat to combine security and customs checks for passengers of international flights to reduce delays caused by worsening congestion.

According to the Civil Aviation Authority of Vietnam (CAAV)'s order, the new procedure will be introduced sometime this month.

It said the Ho Chi Minh City airport will have to create double-purpose checkpoints and report the process next week.

A graphic map of Tan Son Nhat Airport's international terminal. Photo credit: hochiminhcityairport.

The similar change will also be applied at other airports with international flights, including those in Hanoi and Da Nang, by the end of the year, the authority said.

Since 2013, Tan Son Nhat has operated above its designed capacity of 20 million passengers a year.

Last year, it received more than 22 million, and the number of passengers was expected to exceed 25 million this year.

Local aviation officials have blamed congestion which plagues both domestic and international terminals for the airport's infamously poor service quality.